Unusual aluminum chloride-assisted conversion of isopropenyl acetate into 3-acetyl- and 3,5-diacetyl-2,6-dimethyl- 4 H-pyran-4-ones.

Reflux of isopropenyl acetate with an excess of AlCl in 1,2-dichloroethane affords 3,5-diacetyl-2,6-dimethyl-4 H-pyran-4-one in 17% yield. The mild acidic cleavage of the latter (2% HCl, 20 °C, 16 h) gives 3-acetyl-2,6-dimethyl-4 H-pyran-4-one in 87% yield, whereas this reaction under more drastic conditions (17% HCl, reflux, 3 h) gives 2,6-dimethyl-4 H-pyran-4-one in 61% yield. [ABSTRACT FROM AUTHOR]